A method by which a molten resin mass is compression molded by coaction of a female die and a male die of a metal die is known as a method for molding synthetic resin containers such as PET bottles and closures from synthetic resins for closing the mouth sections of the containers. It is possible to mold a molten resin mass to a final container shape by compression molding, or to mold the mass to a pre-molded body (referred to hereinbelow as “preform”) for a container and then mold the preform to the final container shape via a subsequent process such as blow molding. When a container is molded, a molten resin extruded from an extruder is cut to obtain a molten resin mass of a column-like shape that falls into a cavity formed in a female die. The molten resin mass located inside the cavity is compression molded by pressing a male die, which is a metal die core, into the molten resin mass, thereby molding the mass into a preform or a final container shape between the female die and the male die. When a closure is molded, similarly to container molding, a molten resin mass is cut from a molten resin, and the molten resin mass is dropped into a cavity in a female die and molded to a final shape of the closure or a pre-molded body thereof.
In order to improve functionality, for example, gas barrier properties and mechanical properties of containers or container lids using synthetic resins as starting materials, or to enable the use of inexpensive recycled resins, multilayer resin starting materials comprising an auxiliary resin layer having the aforementioned properties as an intermediate layer on the inner side of a main resin layer have been often used in the past. In such case, molten resin mass supplied to compression molding are cut from an extruder as composite resin mass comprising these resins. For example, devices in which resin channels for feeding the resins merge in an extrusion channel, an intermittent pressurizing mechanism is provided between an intermediate layer resin extruder and an intermediate layer resin channel, and an intermediate resin layer that is extruded intermittently is sealed in a drop-like form inside the inner and outer layer resins. (Ref. Patent Documents 1-3)
Patent Document 1:
    Japanese Publication of Examined Application No. 2-60499Patent Document 2:    Japanese Published Patent Application No. 2003-39531Patent Document 3:    Japanese Published Patent Application No. 2003-33964
The composite molten resin mass that can be formed with such extrusion feed devices are limited to mass in which an auxiliary resin of one type is enclosed in an outer resin that is a main resin and mass in which auxiliary resins of two types are enclosed in the outer resin in inclusion relation with each other, as shown in FIG. 11-A. For example, as a composite resin mass comprising three resins, a multilayer molten resin mass 110 composed of resins of three types, namely, a main resin 111 and auxiliary resins 112, 113 that are in inclusion relation in a sequence from the outside to the inside, is formed as an intermediate product, as shown in FIG. 11-A. Where the multilayer molten resin mass 110 is compression molded with a die molding apparatus 120 comprising a female die 121 and a male die 122, as shown in FIG. 11-B, a container 130 can be formed that comprises a total of five layers of three types, namely, outermost resin layers 126, 126 comprising the main resin 111, intermediate resin layers 127, 127 comprising the first auxiliary resin 112, and a resin layer 128 that is an innermost layer comprising the second auxiliary resin 113. With the method for molding the resin mass, only a layer configuration that is symmetrical in the thickness direction, as shown in FIG. 11-C, can be molded as a wall portion 131 of the container 130. Such molded products do not necessary meet a demand for increased variety of layer configuration.
For example, where a resin having an oxygen barrier ability is used as the first auxiliary resin and a resin having a moisture barrier ability is used as the second auxiliary resin to obtain a container having an oxygen barrier ability and a moisture barrier ability, the composite resin mass obtained with the above-described conventional extrusion feed devices is as shown in FIG. 11-A, and the wall configuration of the container obtained by compression molding the composite resin mass is a five-layer configuration having two oxygen barrier resin layers, as shown in FIG. 11-C. Therefore, each oxygen barrier layer has to be decreased in thickness correspondingly to the necessary amount of resin, a suitable layer thickness cannot be obtained and the container can be ruptured during use or a sufficient oxygen barrier function cannot be ensured. These problems can be resolved by increasing the amount of resin with oxygen barrier ability, but the cost increases accordingly. Yet another resultant drawback is that the wall thickness of the container becomes larger than necessary. The problem can be effectively resolved by configuring each layer composed of an auxiliary resin having the desired functionality of respective individual layers, but such a resolution is impossible with the conventional extrusion feed devices for a composite resin extrusion material because, as described above, other resin layers, except an auxiliary resin positioned in the center zone, are always in the form of two layers disposed symmetrically with respect to the center section in the thickness direction. Therefore there is a need for a device making it possible to feed resin extruded materials of multiple types into a single discharge passage so that the feed position and feed period of each extruded material can be selected appropriately and to form composite resins having a variety of layer configurations in which resin layers can be arranged arbitrarily.